News - April 26, 2007

North Vietnamese agriculture not sustainable

Rapidly expanding agriculture is causing soil degradation and water pollution in northern Vietnam. According to Dr Mai Van Trinh, agriculture is a serious danger to the quality of natural resources, and an integrated analysis of all forms of land use is necessary if land use is to become sustainable.

Van Trinh did his research in the Tam Duong district, in the upper reaches of the Red River, where three different landscapes and cultivation are found. On the plains rice and vegetables are grown, in the hillier areas cassava, maize and soya beans, and in the northern hilly area there is a productive forest with eucalyptus trees. Van Trinh regards the erosion as a consequence of the expanding farming activities. Planting the eucalyptus trees reduced erosion for a while, but once the trees were harvested erosion became worse. Van Trinh calculated that soil loss in 2004 was 163 kg/ha and 1722 kg/ha in 2005.

In addition to erosion, leaching of nutrients from the soil is a big problem in the Tam Duong district. This has been made worse by farmers starting to grow added-value crops, which need large amounts of artificial fertilizers. Losses due to leaching from flower cultivation were 193 kg nitrogen per hectare, for vegetables the figure was 115 kg/ha, whereas one hectare of rice is only responsible for about 50 kg of nitrogen leaching.

To determine the effect of growing different crops on the natural resource base, Van Trinh developed a nitrogen balance model that simulates the nitrogen dynamics at regional level. This showed that leaching is the most important form of nutrient loss. Van Trinh thinks the model can be used to calculate the environmental effects of different forms of land use, and can therefore also be used for landscape planning. Only with an integrated comparison of all environmental effects can you move towards sustainable production, says Van Trinh. /Martin Woestenburg

Mai Van Trinh received his PhD on 17 April. His promotor was Professor Herman van Keulen, chair of Plant Production Systems.